Fuel cells produce electricity through electrochemical reaction and have been used as power sources in many applications. Fuel cells can offer significant benefits over other sources of electrical energy, such as improved efficiency, reliability, durability, cost and environmental benefits. Fuel cells may eventually be used in automobiles and trucks. Fuel cells may also power homes and businesses.
There are several different types of fuel cells, each having advantages that may make them particularly suited to given applications. One type is a proton exchange membrane (PEM) fuel cell, which has a membrane sandwiched between an anode and a cathode. To produce electricity through an electrochemical reaction, hydrogen (H2) is supplied to the anode and air or oxygen (O2) is supplied to the cathode.
In a first half-cell reaction, dissociation of the hydrogen (H2) at the anode generates hydrogen protons (H+) and electrons (e−). Because the membrane is proton conductive, the protons are transported through the membrane. The electrons flow through an electrical load that is connected across the electrodes. In a second half-cell reaction, oxygen (O2) at the cathode reacts with protons (H+) and electrons (e−) are taken up to form water (H2O). After deactivating a fuel cell stack, the water remains within the flow channels of the fuel cell stack. Under sub-freezing ambient conditions, the water can freeze and possibly damage components of the fuel cell stack. Additionally, the presence of frozen water hinders start-up of the fuel cell stack.
Fuel cell systems generally include additional systems for purging and pre-heating the fuel cell stacks prior to shutdown and during start-up, respectively. The energy required to power these additional systems is generally provide from a battery storage system using an ancillary boost converter. The battery storage system must store a significant amount of energy and is therefore, undesirable due to the volume, mass and cost of such an energy storage system.